Investigators on Thursday morning served a search warrant at a Montebello woman's home amid an ongoing search for her grandson, a 5-year-old South Pasadena boy who was last seen with his father.

The search began about 9 a.m. in the 500 block of Via Val Verde, where investigators "seized various items of evidence" at the residence of Aramazd Andressian Sr.'s mother, according to a statement released by the Los Angeles County Sheriff's Department.

No further description of the evidence was disclosed.

Aramazd Andressian Jr.'s disappearance occurred just over a month ago.

Andressian Sr.'s estranged wife reported their son missing on April 22 after the father neglected to drop the boy off at an agreed-upon meeting location.

Hours later, Andressian Sr. was discovered passed out at South Pasadena's Arroyo Park. His gray 2004 BMW sedan, with California license plate 5FIL646, was found nearby; its interior and exterior had been doused with gasoline.

The man could not account for his son's whereabouts.

The elder Andressian was taken into custody and was later released due to lack of evidence, authorities said.

Detectives serve search warrant at home of grandmother of missing South Pasadena boy Aramazd Andressian. Neighbors say they took a computer. pic.twitter.com/QDnnBiTkZI

Ana Estevez, the child's mother, appeared at a news conference with sheriff's officials on May 17.

"There are no words to describe how heartbroken I am. Although I do not know his whereabouts, I do believe that Piqui is alive, missing his family and desperately wants to come home," the distraught woman said, using her son's nickname. "I am counting the days until I see you again, and I will never stop looking for you."

Anyone with information about Aramazd Andressian Jr.'s whereabouts is urged to call the sheriff's Homicide Bureau at (323) 890-5500 or provide an anonymous tip to Crime Stoppers at (800)222-TIPS.